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Magnesium advice?

01-02-2013, 10:57 PM

Just got asked to fix a crack in a transmission casing made of magnesium alloy (AZ91D). I have never welded magnesium of any kind. Will be using a diversion 165 with pure argon. I was hoping someone could give me some advice on filler material, and any tips or tricks you may know. Should I just prep it like aluminum? Any help appreciated.

Comment

That is pretty questionable. There is just not enough amps in that unit to make that weld.

I too would question whether a Diversion 165 will be capable of performing the weld adequately. However, depending on the location there might be enough power to provide sufficient penetration. You will want to clean the material much similar to aluminum:

Joint prep (if applicable) should be done with a cutting process such as a rotary carbide tool or file (rather than a grinding/flap wheel process)

Repeat steps 1-3 after any joint prep (if applicable)

Preheating will help with puddle fluidity and can increase penetration - I would recommend using a dry heat such as a halogen lamp to introduce the heat into the case (improper use of a torch can lead to condensation, which in turn can cause porosity)

Using the appropriate filler material and adequate settings should produce good results.

Comment

So assuming I have the power, is there a generic Mg filler rod I should use? Is 2% ceriated ok? Should I ball it or grind it to a point. I obviously have no experience with Mg but thought I won't learn without doing.

Thanks for the responses
Tyler

Comment

So assuming I have the power, is there a generic Mg filler rod I should use? Is 2% ceriated ok? Should I ball it or grind it to a point. I obviously have no experience with Mg but thought I won't learn without doing.

Thanks for the responses

Tyler

If this is a repair that somebody's counting on....consider passing for all the good reasons you've already stated.

You need to match the filler to the casting makeup...which is ???

Run the ceriated with a point, for starters. Mg doesn't weld at all like AL, BTW.

At this point, you need to check on price and availability of possible
Mg fillers....sticker shock.

Either post pics of the crack and total casting or at least give description of where it is.

Comment

Tyler you may get away with using your Diversion 165 as you don't need as many amps with Magnesium compared to Aluminium.
Use a die grinder with a coarse cutter and you'll find it doesn't clog up like Aluminium does to grind a groove where you need to weld.
Also use the die grinder to clean away the "skin" of the casting adjacent to the weld groove to ensure your weld area is clean.
The weld will be dirty there's no way around it but you have to be persistent especially with castings and if means grinding out welds till you get a reasonable run in the groove then that's what has to be done.
The weld will look smutty and dirty while your welding it but with a quick wire brush it comes up pretty good.
Because of your amperage limitations start on the thinner sections and weld towards the thicker sections to allow the heat to radiate and build up heat in the casting.
We weld Magnesium Sprintcar diff centres and it's often the quality of the casting that's the limiting factor, sometimes the casting won't weld regardless of what I try but I'm upfront in telling customers I don't know how a casting will weld until I actually start welding it.
For filler wire we use AZ92A, it's a pretty good all round Mag filler wire but be warned "it's expensive".
Don't use gas lenses, the cr@p thrown up by the arc will clog a gas lens pretty quick just use standard Tig collets and ceramics.
Hope this helps.
Regards Andrew from Oz.

Comment

4x4 gave you some good advise, But I'd like to add a few things.
4x4 you might want to try this the next time you get an oil soaked case.

If your dealing with a thinner section 3/16 or less dont vee groove, Use a stainless wire wheel on a die grinder to clean the top coating after you degrease, Then go over the crack with your tig torch with a few less amps than what you would typically weld it at ( Doing this will help pull the conatamination to the top )
Then use the wire wheel to clean the joint, repeat this process up to 3 times.

Then turn your amps back up, grab some rod and go at it.

Good luck.

Comment

For an inexpensive practice surface, stop by any auto junkyard & look for a fullsize truck transfer case from ~'85-up. Most BorgWarner t-cases have been Mg since then, and the BW1356 found in '86-96 F-series & Broncos are VERY common & cheap.